The invention relates to a method of and apparatus for measuring defects in the sealing of closures or the like, particularly of bottle caps, wherein a sealing mass is applied, in the closure area, to the base of the cap.
Container closures, for example, closures of bottles, must meet stringent requirements. The first requirement consists, independently of the shape of the closures and regardless of whether they are screw caps with a high edge or cap closures with a low edge, for example, crown cork closures, in that the closure must seal the container or the bottle, even at relatively high pressures, in a fully satisfactory manner. In carbonic acid gas-containing liquids, for example, pressures in excess of atmospheric pressure of 5 to 6 atmospheres may occur. The elastic sealing inserted in the base of the closure must therefore be faultless, at least in the closure area between the bottle edge and the inside of the closure.
The danger of a faulty sealing is always particularly great when the caps manufactured on the assembly line are not provided with punched-out sealing platelets, for example, cork discs or the like, but when the sealing is produced by the injection of a liquid sealing mass. This is due to the fact that, whereas the punched-out sealing platelets can be tested for accuracy before being inserted into the closures, and by the use of only faultless sealings a closure waste can be avoided, control in the case of the use of a liquid sealing mass can be carried out in finished caps only. The visual testing of closures, as it is presently customary in assembly lines for the closing of bottles, for accuracy in the sealing area is, however, substantially complicated for the following reasons. With the usual production speeds of about 10 caps per second, it is not possible for the human eye to cover each individual cap during a time period necessary for the control. The finished closures are therefore conveyed, in rows of about 20 pieces per row, to a slowly moving conveyer belt, so that the observer can test several caps simultaneously. At a longer observation period, however, the natural fatigue occurs, so that defects are overlooked. Since it also scarcely is possible to look vertically into the closures, the side of the cap that faces the observer, and thus the sealng area positioned at this location, is more or less concealed, depending on the height of the cap edge and on the angle of inspection relative to the cap base, so that defects occurring at this location are not discovered.
The defects existing in the sealing area may also result from too much or too little sealing mass being present in the sealing area which, in the case of bottles, is ring-shaped. While too large a sealing mass is generally not harmful since the elastic sealing, when the cap is pressed against the bottle edge, is elastically deformed and seals the bottle, it is absolutely necessary to avoid defects characterized by too little or a lack of sealing material, since the pressure can escape from the bottle at these locations.